class Solution:
    def combine(self, n: int, k: int) -> List[List[int]]:
        res = []
        def helper(start, comb):
            if len(comb) == k:
                res.append(comb.copy())
                return
            for i in range(start, n+1):
                comb.append(i)
                helper(i+1, comb)
                comb.pop()
        helper(1, [])
        return res